Edward Leung Tin-kei was hammering out his plan to collect nominations from New Territories East residents when the staunch supporter of Hong Kong independence learned about the political bombshell dropped by the Electoral Affairs Commission.

Swinging into action less than 48 hours before registrations formally opened last week for candidates hoping to contest the Legislative Council elections on September 4, the commission threw out a new hoop for aspirants to jump through.

All those wishing to enter the race now have to sign a new declaration that they acknowledge Hong Kong is part of China and that no constitutional amendments can alter the political status quo.

While the form is for all candidates to sign, there is little doubt that the commission is directing its efforts at pro-independence candidates such as Leung.

However, the move risks opening the floodgates to all manner of legal and political challenges.

Leung and many moderate pan-democrats his group despises have already chosen to snub the rule.

They submitted their nomination papers but refused to sign the new declaration.

“If the government ends up rejecting my candidacy and that of other advocates of Hong Kong independence at the expense of social instability, it is no different from waging a war with the Hong Kong public,” Leung warned.

On Friday, it emerged that Leung received an email from electoral affairs officials, asking him whether he was “in fact continuing to advocate and push for Hong Kong independence” despite signing the general statement to uphold the Basic Law. Leung was asked to reply by 11am on Saturday.

It is understood that he will meet officials no later than early next month. He said he would explain his position to the media on Saturday.

Both Beijing and the Hong Kong government are viewing with increasing wariness the actions and ideology of the 25-year-old who has been accused of inciting the Mong Kok riot.

In February, as the city grappled with the aftermath of the worst violent incident for more than 30 years, Leung calmly went on to campaign in a Legco by-election. He garnered 66,000 votes, a respectable showing considering he was a political nonentity just months before that.

The number of votes he won has become a measure not only of the level of dissatisfaction among Hongkongers towards the current administration, but also interest in the idea of setting up a separate sovereign state.

Not long after the by-election, several university students formed the provocatively named Hong Kong National Party with the clear aim of seeking independence.

Before the new rule was announced, interest in such groups centred mostly on where they would win votes – from pan-democrats, the smaller radical fringe or, most unlikely, the pro-government camp.

Now, with the declaration requirement, more questions have surfaced: Will their rhetoric be heard in the coming weeks of electioneering? If so, how will the commission act and with what consequences? How will voters respond? And will sympathy deepen or dwindle for the localists or at least the pan-democrats?

The declaration is in addition to an existing one on upholding the Basic Law, which has been in place since 1997. It specifically lists Articles 1, 12 and 159 (4) of the Basic Law.

Article 1 states that Hong Kong is an inalienable part of the People’s Republic. Article 12 says Hong Kong comes directly under the central government and Article 159(4) that no amendment to the Basic Law shall contravene Beijing’s established basic policies regarding the special administrative region.

“To put it plainly, there are some people promoting and pushing for Hong Kong independence,” Chief Secretary Carrie Lam Cheng Yuet-ngor said of the new election rule. “It is obvious there is something that is contrary to ‘one country, two systems’ and the Basic Law. We can’t pretend we’re not seeing it.”

Beijing’s top man in Hong Kong, liaison office chief Zhang Xiaoming, went further, saying the need to stop pro-independence activists from being elected into the legislature was a matter not only of the law, but also of “right and wrong”.

“This is not just a technical and legal matter,” Zhang said, “but also one of right and wrong, bottom line and principle.”

Critics have compared the new declaration rule to a bid to silence independence advocates in Scotland or Catalonia, a move London and Madrid would have serious qualms about taking.

But China is not England or Spain. Hong Kong is a part of China under the “one country, two systems” model. It enjoys a high degree of autonomy but also faces a central government that has never countenanced secessionist tendencies from any part of its domain.

As it is, the rules already require a candidate to affirm the “one country, two systems” model, as spelt out in the Legislative Council Ordinance. Under Section 40, “the nomination form includes ... a declaration to the effect that the person will uphold the Basic Law and pledge allegiance to [Hong Kong].”

That was broader than what the government was now pursuing with the new rule, Anson Wong Man-kit, chairman of the Bar Association’s constitutional affairs and human rights committee, said.

The new declaration “is an unbelievable object born out of nowhere”, Civic Party chairwoman Audrey Eu Yuet-mee said.

“Why doesn’t the document ask lawmakers to pay attention to the Basic Law provision on [the Legislative Council] quorum given the pro-establishment lawmakers’ tendency not to show up in the past four years?” an adviser to a pan-democratic lawmaker asked on Facebook.

The legal effect of signing the new declaration appears clear. If candidates breach the rule by speaking about independence, they could be hauled up for making a false declaration – an offence with a maximum penalty of two years in jail under the Crimes Ordinance – according to Wong of the Bar Association. His view was shared by former justice secretary Elsie Leung Oi-sie, who is now the vice-chairwoman of the Basic Law Committee under the National People’s Congress Standing Committee.

But what happens if the lawmaker who signed the declaration changes his tune the moment he is elected or has a change of heart two years later?

The minister handling constitutional matters suggested that a signature on the document would be legally binding for good. “If someone voluntarily signs a declaration that carries with it legal ... liability and consequences ... I believe he should have a consistent stance of upholding the Basic Law no matter under what circumstances or in what ways,” Secretary for Constitutional and Mainland Affairs Raymond Tam Chi-yuen said.

But Jonathan Man Ho-ching of the pan-democrat Progressive Lawyers Group questioned whether the scope of free speech would be limited if officials pursued a candidate based on a signature.

If someone doesn’t sign the declaration – as most pan-democrats vow to do – all manner of legal challenges could be the next game in town.

Barnabas Fung Wah, the High Court judge who chairs the Electoral Affairs Commission, reportedly said during a meeting with pan-democrats: “If you don’t sign it, it doesn’t necessarily mean you’ll be disqualified.”

With that statement, Fung has allowed a rule to be bent for some but not others. Of course, the political argument to be made is that veteran pan-democrats who have served Hong Kong’s legislature since the colonial era have long accepted the Basic Law framework and so cannot be said to be in breach of the rule.

After all, even the country’s third-ranking official, Zhang Dejiang, met four moderate pan-democrats during his visit to Hong Kong in May, drawing a line between them and pro-independence secessionists.

In those circumstances, Beijing could issue an interpretation of the Basic Law ... There are many political possibilities

Political scientist Ivan Choy

But a rule should apply to all equally, critics point out, as they lament the murkiness of official statements about the new declaration.

“If someone is disqualified, there must be a legal foundation,” said Democrat candidate Sin Chung-kai. “Rule of law is what defines Hong Kong.”

On the record, Fung said that it would be a matter for the returning officer or, when necessary, the Department of Justice to decide whether failure to sign the declaration amounted to an incomplete nomination process.

Such wide discretion could well trigger a chain of events leading to a constitutional crisis. If a pro-independence candidate is rejected, he would most certainly lodge an election petition with a court in a bid to override the result. The court might find itself having to wade into not one but several such cases.

“In those circumstances, Beijing could issue an interpretation of the Basic Law,” said Ivan Choy Chi-keung, a political scientist at Chinese University, in reference to the power of the National People’s Congress Standing Committee. In the past, when the Standing Committee made interpretations, its role was viewed negatively. “There are many political possibilities,” Choy said.

Those possibilities are likely to turn the Legco election into the most contentious yet. Unless cooler heads prevail in the coming weeks, the new declaration may become the tinder for a bigger conflagration on the Hong Kong political scene.